In order to meet the requirement that the dynamics star simulators based on liquid crystal on silicon splicing reduce the stray light in the background, the traditional optical engine were optimized. A method of combining multiple polarization beam splitter into one components was proposed to optimize optical engine, and the design of the optical-mechanical structure was made. This paper expounded the design scheme of lighting system for optical engine, and we elaborated the method of reducing the field-of-view angle and increasing the uniformity. The lighting optical system was simulated by Tracepro, and the feasibility of the programme was verified. According to the results we can get that the stray light irradiance of the dynamic star simulator was reduced by 2.93 times after optimization, hence, the optimized optical engine effectively suppresses the stray light of background, and improved the consistency of the contrast ratio between the two pieces of liquid crystal on silicon.